So.. to connect your dreamcast to the internet over dialup, you can just plug the modem straight into the phone socket without a router?

Here in the UK, I get my 'fibre' broadband through a special connection in the house rather than ADSL over the phoneline. This means my phone socket is going unused (I don't have a house phone), but the line should be active because I have to pay line rental. So in theory I could connect my dreamcast straight to the phone line without stopping the house's broadband connection.